Figure 1. Pacific Giant Salamander (Credit: Sierra Nystrom)
Figure 2. The Mack Creek study site is located in the HJ Andrews Experimental Forest, Oregon. (Credit: Dana Warren)
Figure 3. Mack Creek, HJ Andrews Experimental Forest, OR (Credit: Oregon State University)
| Channel Class | Clear Cut | Old Growth |
|---|---|---|
| Cascade | 247 (55%) | 201 (45%) |
| Pool | 31 (41%) | 45 (59%) |
| Side Channel | 90 (55%) | 74 (45%) |
##
## Pearson's Chi-squared test
##
## data: chi_sal_counts
## X-squared = 5.5413, df = 2, p-value = 0.06262
There is not a significant association between forest condition (old growth/clear cut) on where in the channel salamanders are found (pool/side-channel/cascade) for salamanders sampled in 2017. (\(\chi\)2(2) = 5.54, p = 0.063).
##
## Welch Two Sample t-test
##
## data: weight_ttest_og and weight_ttest_cc
## t = -1.6669, df = 692.79, p-value = 0.09599
## alternative hypothesis: true difference in means is not equal to 0
## 95 percent confidence interval:
## -2.5972032 0.2121307
## sample estimates:
## mean of x mean of y
## 6.583333 7.775870
##
## Cohen's d
##
## d estimate: 0.1259284 (negligible)
## 95 percent confidence interval:
## lower upper
## -0.0234303 0.2752870
There is not enough evidence to conclude that mean Pacific Giant Salamander size in the clear cut section of Mack Creek in 2017 (7.78 \(\pm\) 9.9, n = 368) differed significantly from mean Pacific Giant Salamander size in the old growth section of Mack Creek in 2017 (6.58 \(\pm\) 8.96, n = 327) by a two-sided, two sample t-test (t(692.79) = -1.67, p = 0.096). In addition, the effect size between mean sizes is negligible (Cohen’s d = 0.13).
## Levene's Test for Homogeneity of Variance (center = median)
## Df F value Pr(>F)
## group 2 2.3883 0.09255 .
## 684
## ---
## Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
## Df Sum Sq Mean Sq F value Pr(>F)
## channel_class 2 757 378.4 4.216 0.0151 *
## Residuals 684 61403 89.8
## ---
## Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
## 1 observation deleted due to missingness
## Anova Table (Type II tests)
##
## Response: weight
## Sum Sq Df F value Pr(>F)
## channel_class 757 2 4.2156 0.01515 *
## Residuals 61403 684
## ---
## Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
## Tukey multiple comparisons of means
## 95% family-wise confidence level
##
## Fit: aov(formula = weight ~ channel_class, data = sal_weights_class)
##
## $channel_class
## diff lwr upr p adj
## Pool-Cascade 1.776650 -0.9846147 4.5379145 0.2862119
## Side Channel-Cascade -1.844204 -3.8759182 0.1875106 0.0841989
## Side Channel-Pool -3.620854 -6.7089770 -0.5327303 0.0166225
## Call:
## aov(formula = weight ~ channel_class, data = sal_weights_class)
##
## Terms:
## channel_class Residuals
## Sum of Squares 756.87 61403.22
## Deg. of Freedom 2 684
##
## Residual standard error: 9.474745
## Estimated effects may be unbalanced
## 1 observation deleted due to missingness
##
## Cohen's d
##
## d estimate: 0.2088538 (small)
## 95 percent confidence interval:
## lower upper
## 0.02917986 0.38852765
Mean salamander weight (g) differed significantly between the side-channel and pool channel classifications (one-way ANOVA with post-hoc Tukey’s HSD, F(2, 684) = 4.22, p = 0.015). Although mean salamander weight differed significantly, the effect size is small (Cohen’s d = 0.21).
Gregory S. V. 2016. Aquatic Vertebrate Population Study in Mack Creek, Andrews Experimental Forest, 1987 to present. Environmental Data Initiative. https://doi.org/10.6073/pasta/5de64af9c11579266ef20da2ff32f702. Dataset accessed 11/27/2019.